1. Field of the Invention
The present invention relates to a display device comprising light emitting elements, a driving method thereof and an electronic appliance.
2. Description of the Related Art
In recent years, display devices comprising light emitting elements typified by EL (Electro Luminescence) elements have been developed, and wide applications thereof are expected by utilizing the advantages such as high image quality, wide viewing angle, thin shape and light weight. A light emitting element has a property that luminance thereof is proportional to a current value supplied thereto. Therefore, in order to display gray scales accurately, there has been proposed a display device using a constant current drive where a constant current is supplied to the light emitting element.    [Patent Document 1] Japanese Patent Laid-Open No. 2003-323159
A light emitting element has a property that a resistance value (internal resistance value) thereof changes according to the ambient temperature. Specifically, assuming that the room temperature is a normal temperature, when the ambient temperature becomes higher than the normal temperature, a resistance value decreases, and when the ambient temperature becomes lower than the normal temperature, on the other hand, a resistance value increases. Therefore, when the ambient temperature becomes higher, a current value increases, leading to a higher luminance than the desired luminance, and when the ambient temperature becomes lower, on the other hand, a current value decreases, leading to a lower luminance than the desired luminance. Such a property of a light emitting element is shown in a graph (FIG. 33A) illustrating a relationship between V-I characteristics of a light emitting element and temperatures. Also, the light emitting element has a property that a current value thereof decreases with time. Such a property of a light emitting element is shown in a graph (FIG. 33B) illustrating a relationship between V-I characteristics of a light emitting element and time.
When the ambient temperature changes or degradation is caused with time due to the properties of the light emitting element as set forth above, luminance thereof varies.